Analysis of autoxidized fats by gas chromatography-mass spectrometry: X. Volatile thermal decomposition products of methyl linolenate dimers.

High-molecular weight compounds previously were found to be important secondary products from autoxidation of polyunsaturated fatty esters. The contribution of dimers to oxidative deterioration was investigated by analyzing their volatile thermal decomposition products by capillary gas chromatography-mass spectrometry. Dimers were isolated by gel permeation chromatography from autoxidized linolenate and from the corresponding monohydroperoxides, cyclic peroxides and dihydroperoxides. Major volatile decomposition products identified from these oxidative dimers were similar to those formed from the corresponding monomeric hydroperoxides. However, dimers from linolenate hydroperoxides produced more propanal and methyl 9-oxononanoate than the corresponding monomers but less methyl octanoate and much less or no 2,4-heptadienal and 2,4,7-decatrienal. Significant differences in minor volatile products also were observed between dimeric and monomeric products of methyl linolenate oxidation compounds. Mechanisms are suggested for the formation of volatile decomposition products from different dimeric structures. These dimers are believed to be important sources of volatile compounds contributing to flavor and oxidative deterioration of fats.